iitbombay report
TRANSCRIPT
Maximum Power Point Tracking in Maximum Power Point Tracking in Solar PV Systems
CEP Course on “Converter Topologies for Grid Connected PV System”
Prof Suryanarayana DoollaProf. Suryanarayana DoollaDept. of Energy Science and EngineeringIndian Institute of Technology Bombay
OutlineOutline
Need of MPPT and its History
Various Techniques
Analysis
SSummary
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Need of MPPTNeed of MPPTPV power is increasingly connected to grid
Large ScaleLarge ScaleSmall Scale
Efficiency of Solar PV CellsEarliest MPPT methods published in 1960sSeveral methods are proposed in literature
Direct methodIndirect method
Short Circuitt Open Circuit Short Circuitt, Open Circuit Prior evaluation of panel, based on mathematical relationships, Database not valid for all operating and meteorological conditions
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Maximum Power Point TrackingMaximum Power Point TrackingTo automatically find the voltage (VMPP) or current (IMPP) at which a PV array should current (IMPP) at which a PV array should operate to obtain the maximum power output (PMPP)under a given temperature and irradiance.
Partial shading conditionsIt is possible to have multiple local maxima, but overall there is still only one true MPP.
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TopologyTopology
Load
dc/dc converter Storage
Next Stage
Inverter Grid
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MPPT
Choice of MPPT TechniqueChoice of MPPT TechniqueImplementation complexitySensors requiredSensors requiredAbility to detect multiple local maximaCostCostApplicationResponse timeResponse time
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I-V CurveI V Curve
I-V Characteristics at four different radiation levels I-V Characteristics for three different
temperature levels
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P-V CurveP V Curve
P-V Characteristics at four different radiation levels
P-V Characteristics for three different temperature levels
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Indirect Methods (quasi seeks)Indirect Methods (quasi seeks)MPP is estimated from
Voltage Current The irradianceUsing empirical dataUs g e p c d tMathematical expressions of numerical approx.
The estimation is carried out for a specific PV generator installed in the systemgenerator installed in the systemSome Techniques
Curve fitting methodLookup table methodFractional OC methodFractional SC method
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Direct Methods (true seeking)Direct Methods (true seeking)Use voltage and/or current informationPrior knowledge of PV panel is not requiredPrior knowledge of PV panel is not requiredIndependent of isolation, temperature and degradation levelsgComputational intensiveSome Techniquesq
Hill climbing/P&OIncremental ConductanceFuzzy Logic ControlSlide Control Method
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Fractional Open-Circuit VoltageFractional Open Circuit VoltageNear linear relationship between VOC and VMPP
k1 is a constant of proportionality (0.71-0.78)and depends on
h t i ti f th PV b i dcharacteristics of the PV array being usedcomputed beforehand emperically
VMPP and VOC for specific PV array at different irradiance and temperaturep
Once k1 is known, VOC is measured by shutting down the converter, periodically.
Power loss associated with shutting downPilot cells can be used parallellyPV array never operates at MPP (approximation)Not valid in case of partial shading
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g
Source: H.-J. Noh, D.-Y. Lee, and D.-S. Hyun, “An improved MPPT converter with current compensation method for small scaled PV-applications,” in Proc. 28th Annu. Conf. Ind. Electron. Soc., 2002, pp. 1113–1118
Hill Climbing/Perturb & Observe TechniqueHill Climbing/Perturb & Observe TechniqueIncrementing the voltage increases the power when operating on the left of the MPP and decreases the power when on the right of the MPP.Hill climbing involves a Hill climbing involves a perturbation in the duty ratioP&O a perturbation in P&O a perturbation in the operating voltage of the PV array
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Flow Chart for P&O AlgorithmFlow Chart for P&O Algorithm
13Source: I. Houssamo et al. / Electrical Power and Energy Systems 46 (2013) 98–107
Hill Climbing/Perturb & Observe TechniqueHill Climbing/Perturb & Observe TechniqueHill climbing and P&O methods can fail under rapidly changing atmospheric conditionsIf the irradiance increases and shifts the power curve from P to If the irradiance increases and shifts the power curve from P1 to P2 within one sampling period, the operating point will move from A to C.A three-point weight comparison P&O
Compares the actual power point to two preceding ones before a decision is made about the perturbation sign
Can be implemented using Can be implemented using digital/analog circuitryTwo sensors are required to implementimplement
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Hill Climbing/Perturb & Observe TechniqueHill Climbing/Perturb & Observe TechniqueThe process is repeated periodically until the MPP is reached.MPP is reached.The system then oscillates about the MPP.
The oscillation can be minimized by reducing the y gperturbation step size. Smaller perturbation size slows down the MPPT. Variable perturbation size that gets smaller towards Variable perturbation size that gets smaller towards the MPP
Fuzzy logic control is used to optimize the magnitude of the next perturbation.
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Incremental ConductanceIncremental ConductanceBased on fact that the slope of p-v
Zero at MPPNegative on right of MPPPositive on left of MPP
The MPP can e tracked by comparing the instantaneous conductance (I/V ) to the incremental conductance
The algorithm can instantly calculate i/v and di/dv to deduct the direction of the perturbation leading to the MPP
16 K. H. Hussein and I. Mota, “Maximum photovoltaic power tracking: An algorithm for rapidly changing atmospheric conditions,” in IEE Proc. Generation Transmiss. Distrib., 1995, pp. 59–64.
Comparison- P&O and INC MethodsComparison P&O and INC MethodsConcerning power efficiency, theoretically, INC method could provide a better tracking of MPP than P&O algorithmDue to the noise and error measurements it is difficult to satisfy some of the equationsIt produces oscillations around the MPP and power lossComplex to implement when compared to P&OTracking step value has a significant effect on effectiveness of MPPTMPPTWhen tracking step value is chosen correctly, P&O can have an energy efficiency equivalent to that obtained with INCModified to obtain MPP even in partial shading conditionsModified to obtain MPP even in partial shading conditions
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Major Characteristics - ComparisonMajor Characteristics ComparisonTechnique Array
dependent
True MPPT?
Analog or Digital
Periodic Tuning
Convergence Speed
Implementation Complexity
Sensed parameters
ndent
P&O NO YES Both NO Varies Low V, I
INC NO YES Digital NO Varies Medium V, I
FracVOC YES NO Both Yes Medium Low V
Frac ISC YES NO Both Yes Medium Medium I
RCC NO YES Analog NO Fast Low V, I
dp/dv or dp/di
NO YES Digital NO Fast Medium V, I
Impp and Vmpp
YES YES Digital Yes N/A Medium Irradiance, temperatureVmpp temperature
OCC Yes No Both Yes Fast Medium Current
Current Sweep
Yes Yes Digital Yes Slow High V, I
18 Source: T. Esram, and P. L. Chapman, “Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques,” IEEE transactions on energy conversion, vol. 22, no. 2, june 2007.
ApplicationsApplicationsSpace and Orbital Stations
Cost and complexity are not an issue,p y ,High Reliability and performanceHill climbing/P&O, IncCond, and RCC are appropriate
S l hi lSolar VehiclesRequire fast convergence to MPPFuzzy logic control, neural network, RCC, load current or Fuzzy logic control, neural network, RCC, load current or load voltage maximization may be considered
Residential UseP i l h di i b k iPartial shading issues, payback timeTwo stage incremental conductance, current sweep methods, OCC MPPT
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ApplicationsApplicationsStreet lighting
Charging of batteries during the dayCharging of batteries during the dayEasy and cheap implementation is more importantFractional VOC and/or Fractional ISC
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